The present invention relates to a wear indicator for disc brakes and, in particular, to a wear indicator that can be examined by physical contact (i.e., touch) where space permits and by eyesight and which thus permits inspection with regard to both the brake pads and rotor (hereinafter collectively referred to as the friction couple).
Disc brake assemblies for vehicles such as passenger cars and trucks are of generally well known construction and typically include a caliper, brake pads, a rotor and related hardware. The caliper is mounted in a carrier for back and forth sliding motion so that inward motion of the caliper when acted upon fluidically (air or other fluid) by operation of the vehicle brake pedal pushes the associated brake or friction pad into the revolving rotor associated with the vehicle wheel to be braked. The brake pads are typically steel plates to which heat-resistant (e.g., organic or metal-particle filled) friction material is joined by riveting, bonding or the like. The rotors are typically made of cast iron. Conventional examples of disc brake assemblies and their components are shown in U.S. Pat. Nos. 4,446,948; 6,811,002; and 6,910,554. Air disk brakes of the type used in commercial vehicles are also currently marketed by Bendix Commercial Vehicle Systems and WABCO Vehicle Control Systems, the construction of which is well known to those of ordinary skill in this field. Other examples of an air brake assembly are described in U.S. Pat. Nos. 4,022,300; 4,094,388, and 6,230,851.
Safety and cost considerations dictate that the condition of vehicle disc brake friction couple be regularly monitored and readily ascertainable. The ability to visually observe a pad wear indicator in a cost effective way is often defeated by various vehicle suspension components in addition to the associated wheel and tire. In addition, attention has been focused on the past on observing the amount of pad wear but not the amount of rotor wear which is less evident and not usually as rapid as pad wear.
In the past, it has been known to employ is vehicle brake systems and other types of machinery as well as to employ systems for indicating a wear condition of brake components such as friction discs and pads. Mechanical or electronic wear sensors have been proposed in truck disc brake systems as described in U.S. Pat. Nos. 5,330,034 and 5,651,430. Vehicle friction couples have also been used in construction machinery as described in U.S. Pat. No. 6,460,659 which proposes a visual brake wear indicator on which the signal indicating excessive wear of the friction material is provided by a pin visible through a window or a signal light activated by a pressure switch. As above indicated, however, visual indicators are often impractical because of sight-line obstructions, and remote sensing introduces an undesirable complexity and cost to the inspection process.
Another currently employed approach is to use the caliper position against a marking on the caliper itself to determine the condition of the brake pads. Still another conventional technique has been to insert a metal pin through a rubber sleeve so that pad replacement and rotor inspection are indicated by the edge of the rubber sleeve becoming flush with the edge of the metal pin. Alternatively, the rubber sleeve could surround the metal pin such that inspection and/or replacement would be deemed necessary when the rubber sleeve curled around the metal pin to a specific location indicated on the sleeve. In any of these cases, however, visual inspection is required but may not be possible, thereby limiting the use of these approaches to certain disc brake environments.
Other examples of disc brake assembly wear indicators or monitoring systems of varying complexity can be found in U.S. Pat. Nos. 3,648,511; 4,356,897; 5,261,508; 5,848,672; 5,931,266; 6,237,723; 6,450,587; 6,691,835; and 6,891,468. These documents are illustrative of the state of the art to which the present invention pertains.
An object of the present invention is to provide a wear indicator that reliably, accurately, and easily allows an inspector to determine either visually or tactilely the amount of wear on the friction couple, not just the friction pads.
The present invention is based upon the recognition that a highly accurate tactile wear indicator that also permits visual inspection can be achieved through the simple expedient of providing markings on the carrier as well as the brake caliper. In operation, these markings are furthest apart when the friction couple is in a new (or unworn) condition and decrease in their distance from each other as the friction couple, not necessarily just the pads, wears by an amount equal to the total wear on the friction couple system.
One advantage of the present invention, therefore, is that it permits inspection by touch where visual observation is not possible.
Yet another advantage of the present invention is that it indicates wear of the friction couple as a whole. Thus, for example, the indicator of the present invention signals the amount of friction couple wear when the pads wear down to a minimum acceptable amount but rotor wear has not occurred (as is sometimes the case with the first set of pads) or where both pad and rotor wear have occurred in combination.
By providing a physical mark such as a raised portion or an indication that is also visually observable between the caliper and carrier castings, inspection of the friction couple wear is now easily achieved as long as there is sufficient space between the brake assembly and the associated wheel for access by an inspector's fingers as, for example, exists with a 24.5 inch wheel and wide-based single wheels.
A still further advantage of the present invention is that inspection time can be significantly reduced without sacrificing accuracy and thereby presenting a reduced operating cost opportunity to customers.
The wear indicator of the present invention further contemplates that visual inspection can be enhanced with chemical markings such as paint or with adhesive stickers. In lieu of raised portions or indentations on the casting, the marking can also be subsequently machined on or ground in the casting.